Confinement Schemes Research Articles

Dynamics of a Centrifugally Confined Fusion Plasma in Space Propulsion Applications

In centrifugal-mirror (CM) confinement, electric and magnetic fields are combined to confine the plasma within a rapidly rotating annulus of burning plasma fixed between two mirror magnets. This confinement scheme can be applied to a direct-fusion-drive propulsion system. Reactor dynamics refers to the thermodynamic and transport characteristics of fusion plasma confined by the centrifugal mirror. The objectives of the paper are to describe 1) the CM well potential and its relation to momentum confinement time, 2) the reactor power balance, 3) the role of electric and magnetic fields in power deposition necessary to affect the plasma rotation, 4) the characteristics and derivation of the critical Mach number for plasma rotation speed, 5) plasma transport in the vicinity of the critical Mach number, and 6) propulsion performance of CM plasmas. The development of these objectives is based on observations and analysis of results from a zero-dimensional (0-D)-model reactor model, where the 0-D model assumes constant properties in the plasma. The principal results are that the power needed to self-power the reactor can be estimated from knowledge of the applied magnetic and electric fields, and the reactor delivers the highest power density when operating near the critical Mach number.

Stress and alignment response to curved obstacles in growing bacterial monolayers.

Monolayers of growing bacteria, confined within channel geometries, exhibit self-organization into a highly aligned laminar state along the axis of the channel. Although this phenomenon has been observed in experiments and simulations under various boundary conditions, the underlying physical mechanism driving this alignment remains unclear. In this study, we conduct simulations of growing bacteria in two-dimensional channel geometries perturbed by fixed obstacles, either circular or arc shaped, placed at the channel's center. Our findings reveal that even sizable obstacles cause only short-ranged disruptions to the baseline laminar state. These disruptions arise from a competition between local planar anchoring and bulk laminar alignment. At smaller obstacle sizes, bulk alignment fully dominates, while at larger sizes planar anchoring induces increasing local disruptions. Furthermore, our analysis indicates that the resulting configurations of the bacterial system display a striking resemblance to the arrangement of hard-rod smectic liquid crystals around circular obstacles. This suggests that modeling hard-rod bacterial monolayers as smectic, rather than nematic, liquid crystals may yield successful outcomes. The insights gained from our study contribute to the expanding body of research on bacterial growth in channels. Our work provides perspectives on the stability of the laminar state and extends our understanding to encompass more intricate confinement schemes.

MCTrans++: a 0-D model for centrifugal mirrors

The centrifugal mirror confinement scheme incorporates supersonic rotation of a plasma into a magnetic mirror device. This concept has been shown experimentally to drastically decrease parallel losses and increase plasma stability as compared with prior axisymmetric mirrors. MCTrans++ is a dimensionless (0-D) scoping tool which rapidly models experimental operating points in the Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland. In the low-collisionality regime, parallel losses can be modelled analytically. A confining potential is set up that is partially ambipolar and partially centrifugal. Due to the stabilizing effects of flow shear, the perpendicular losses can be modelled as classical. Radiation losses such as bremsstrahlung and cyclotron emission are taken into account. A neutrals model is included, and, in some circumstances, charge-exchange losses are found to exceed all other loss mechanisms. We use the SUNDIALS ARKODE library to solve the underlying equations of this model; the resulting software is suitable for scanning large parameter spaces, and can also be used to model time-dependent phenomena such as a capacitive discharge. MCTrans++ has been used to verify results from prior centrifugal mirrors, create an experimental plan for CMFX and find configurations for future reactor-scale fusion devices.

Review of the Short-Term Properties of Confined Seawater Sea Sand Concrete Columns under Compression

The environmental concerns raised by the over-exploitation of fresh water and river sand have driven researchers to explore seawater sea sand concrete (SWSSC) as a substitute for conventional concrete in structural columns. With numerous investigations on this in the past, there is a need to systematically classify and comprehensively understand the response of confined SWSSC columns to promote their usage as structural columns. Consequently, the objective of this review is to summarise and analyse the experimental work conducted so far on confined SWSSC under different compressive loadings. Confined SWSSC columns are classified into five confinement schemes based on the cross-section of the specimens: single-skin, single-skin multilayered, single-skin with additional reinforcement, double-skin, and double-tube-confined SWSSC columns. Based on the findings of the reviewed studies, it can be concluded that the compressive strength and the ductility of the SWSSC can be enhanced through confinement, with effectiveness majorly depending on the material and geometrical properties of the confinement providing material. The existing research work on SWSSC confinement lays out a strong base for future investigations in this area, which will eventually facilitate the acceptance of SWSSC as structural columns, especially for coastal and marine infrastructure.

A novel packing-coupled stress-strain model for confined concrete

To develop low carbon footprint concrete (LCFC) with less CO2 emissions, various minerals (limestone, metakaolin) and industrial waste by-product (fly ash (FA), silica fume (SF), slag) were used to replace cement partially. By optimizing the packing structure, cost-effective, sustainable LCFC with superior strength, workability and durability performances could be achieved. Research studies on fiber-reinforced polymer (FRP) confined LCFC showed that the peak stress, strain at the peak stress and post-peak branch of confined LCFC was far different from that of confined conventional concrete (with cement as the cementitious material only) with the same concrete strength and confinement scheme. To look at this problem more scientifically, this paper conducted experimental and analytical studies about the stress-strain curves of FRP-confined LCFC. A total of 45 concrete column specimens consisting of 15 unconfined concrete and 30 FRP-confined concrete were tested under uni-axial compression. The studied parameters were the thickness of FRP, water- and FA/SF-to-cementitious material ratios. Based on the test results, a novel packing-coupled stress-strain model for confined LCFC has been proposed and verified.

Study The Behavior of Square Reinforced Concrete Columns Strengthened with CFRP

There is a scarcity of research regarding the efficacy of Fiber Reinforced Polymer (FRP) confinement on low strength materials. This paper presents the findings of an experimental study that focuses on the behavior of concentrically loaded short concrete columns with low concrete strength, which are confined using CFRP wraps. A set of nine (9) square concrete columns of short length were subjected to testing. The experimental setup consisted of a single unconfined column, referred to as the control column, and eight additional columns that were confined utilizing externally bonded CFRP wraps. These confining schemes were determined based on the findings of a previous study conducted by the authors, which focused on short square columns with smaller cross sections. The study focused on examining the impact of various confinement schemes on the load carrying capacities of columns through the application of concentric uniaxial compression. The implementation of various confinement schemes led to an increase in the load carrying capacities of confined concrete columns, demonstrating the effectiveness of externally bonded CFRP wraps in enhancing the performance of short rectangular concentrically loaded concrete columns. The primary objective of this investigation is to examine the behavior of concrete columns with reinforcement that have been reinforced using carbon fiber composites. The findings demonstrated the efficacy of carbon fibers in the restoration of impaired columns, as evidenced by a notable enhancement in the load-bearing capacity of the columns, ranging from 35% to 90%.

Fully Electromagnetic Code KARAT Applied to the Problem of Aneutronic Proton–Boron Fusion

In this paper, the full electromagnetic code KARAT is presented in detail, the scope of which is a computational experiment in applied problems of engineering electrodynamics. The basis of the physical model used is Maxwell’s equations together with boundary conditions for fields, as well as material equations linking currents with field strengths. The Particle in Cell (PiC) method for the kinetic description of plasma is implemented in the code. A unique feature of the code KARAT is the possibility of the self-consistent modeling of inelastic processes, in particular, nuclear reactions, at each time step in the process of electrodynamic calculation. The aneutronic proton–boron nuclear reaction, accompanied by the release of almost only α-particles, is extremely in demand in medicine and, perhaps, in the future, will form the basis for obtaining “clean” nuclear energy. The results of a numerical simulation within the framework of the code KARAT of the key physical processes leading to the proton–boron fusion are presented and discussed both for laser-driven plasma and for a plasma oscillatory confinement scheme.

Behaviour of carbon or glass FRP-confined rubberised concrete under monotonic compression

This paper presents a comparative assessment of the compressive behaviour of rubberised concrete (RuC) confined with FRP jackets. In total, three RuC mixes were investigated with rubber content of 6%, 12% and 18% of the total aggregate volume, as well as a conventional concrete mix as a reference. A total of 100 cylindrical concrete specimens (Ø100 × 200 mm) subjected to monotonic axial compression were tested. Confinement scheme comprised 1 or 2 FRP layers of either carbon or glass uniaxial fabric. The mechanical properties, stress–strain behaviour, and confinement effectiveness ratios were assessed. The discussion includes a comparative assessment of the influence of rubber content, confinement and the type of fibre of the fabrics used on the aforementioned properties. The efficiency of analytical models in predicting the experimental results was also investigated. The results revealed a significant reduction of the compressive strength when crumb rubber was used as mineral aggregate replacement in concrete. FRP confinement of RuC was able to mitigate the reduction in compressive strength. Confinement of RuC with glass or carbon FRP jackets having similar axial rigidity resulted in similar stress–strain behaviour, which was mostly affected by the rubber content. Existing analytical models were able to predict the experimental results with moderate accuracy.

Prediction of the additional compressive strength due to PBO-FRCM-confinement of brick-masonry depending on the stiffening effect caused by different discontinuous wrappings: new design-oriented perspective

Fabric Reinforced Cementitious Mortar (FRCM) is an innovative composite system able to strength or rehabilitate masonry members with an efficacy, which is affected by the mechanical and geometrical properties of its constituents: matrix and fabric. Since one of the most appreciated benefits of FRCM is the breathability, the discontinuous application is commonly not considered in the retrofitting. On the other side, the thickness of the matrix may be considerable (ranging between 10 and 30 mm) implying an over-weight and over-stiffness which may influence the seismic response of the structure in a detrimental manner; especially when dealing with column confinement. Consequently, the experimental evidence and the proper design for the partially wrapping with FRCMs is currently lacking.For this reason, the present research reports on an experimental and analytical investigation about PBO (polybenzoxazoles) FRCM-confinement of clay-brick based masonry columns by varying the confinement scheme. The aim is to evaluate the effectiveness of the confinement in terms of axial bearing load capacity and ductility and, at the same time, focusing on the parameters related to the confining scheme showing how these affect the results. Two columns were tested unconfined as lower-bound reference; six columns (i.e. three couples) were partially confined respectively with 3, 4 and 5 wraps having the same width and lastly, a further couple was fully-jacketed as upper-bound reference. The findings evidenced that an appreciable gain in axial strength and deformability was ensured. On the other side, the axial stiffness increased proportionally to the number of confining wraps.Thus, a new analytical model was herein proposed considering the geometry of the confining scheme, as well as the stiffening effect related to it. In particular, a novel effectiveness coefficient (namely KE) is evaluated affecting the theoretical confining pressure based on the axial stiffness of the FRCM confined masonry. The comparison with the own and other available experimental data confirmed the reliability of the proposal which wants to offer a new perspective for the design of the FRCM partial confinement of masonry that needs further investigations to be confirmed by including a variety of masonry and FRCM typologies.

Comparison of core Ar17+ and Mo32+ toroidal rotation in C-Mod plasmas

Core (r/a 0.5) toroidal rotation from argon (Ar17+, 40 AMU) and molybdenum (Mo32+, 96 AMU) ions has been compared in C-Mod tokamak plasmas over a wide range of operating conditions and confinement schemes, including Ohmic L-mode in the linear and saturated regimes, ion cyclotron range of frequencies heated I-mode and H-mode, as well as in discharges with induced locked modes and with external current and rotation drive. In all cases the velocities of the two impurities are identical within about 5%, for a range between −60 and +80 km s−1. This is in general agreement with the predictions of neo-classical theory.

Assessment of the Vortex Feature-Based Vorticity Confinement Method Applied to Rotor Aerodynamics and Aeroacoustics

The accurate prediction of helicopter rotor aerodynamics and aeroacoustics using Computational Fluid Dynamics (CFD) techniques still remains a challenge, as the over-dissipation of numerical schemes results in a higher diffusive rate of rotor wake and vortices than what can be expected from the fluid governing equations. To alleviate this issue, a vortex feature-based vorticity confinement (FVC2-L2) method that combines the locally normalized λ2 vortex detection method with the standard second vorticity confinement (VC2) scheme is presented to counterbalance the truncation error introduced by the numerical discretization of the convective term while avoiding the over-confinement inside the boundary layer. The FVC2-L2 scheme is adopted for helicopter rotor aerodynamic and aeroacoustic predictions through its implementation in the multi-block structured grid CFD solver ROSITA and coupling with the aeroacoustic code ROCAAP based on the permeable surface Ffowcs Williams–Hawkings (PS-FWH) equation. This approach is assessed in helicopter rotor flows via three databases. Firstly, the well-documented HART-II rotor in the baseline condition is used to evaluate the capability of the presented VC scheme in blade–vortex interaction (BVI) phenomena prediction. Subsequently, the UH-1H non-lifting hovering rotor and the AH-1/OLS low-speed descending flight rotor are adopted for assessment of such a method in aeroacoustics. The benefits of the FVC2-L2 scheme in terms of aerodynamics prediction, wake preservation, and noise signal prediction are well demonstrated by comparison with the experimental data and the results obtained without VC schemes. Particularly, the FVC2-L2 scheme mainly improves the highly unsteady airloads prediction, and results in an improvement of BVI noise prediction by more than 5 dB with respect to the case without VC schemes for AH-1/OLS rotor case. Additionally, some shortcomings of the approach are noticed in engineering applications. On the basis of a simplified convective vortex, some provisional guidelines on the required εo value in terms of number of cells per vortex diameter are provided: an εo value ranging from 0.01 to 0.04 for grids which may represent the vortex core diameter with 6 to 12 cells.

Rotating magnetic field configuration for controlled particle flux in material processing applications

Abstract Plasma technology has been an integral part of the semiconductor industries, especially to achieve the desired etch and selectivity of the outcome. These outcomes depend on various factors including the confinement of the charged particles of the plasma source. One of the widely employed confinement schemes is the multipole arrangement of magnetic fields, also known as a multicusp. Such arrangement provides minimum-B field value near the plasma axis and plays significant role in plasma-based ion sources for material processing and in plasma thrusters for spacecraft applications. In the present work, a novel rotating multicusp about its axis is studied to investigate its effect on the confinement of electrons present within it. The multicusp is allowed to rotate with a finite rotational speed, in the range of 0–107 rotation per second, thus inducing an axial electric field. It will lead to a directed axial flux of the electrons, determined by the rotational speed of the multicusp. The dynamics of the electrons enclosed within a rotating multicusp have been studied to explore its radial confinement. The results are of significance for semiconductor industries and others where downstream or afterglow plasmas are utilized for material applications.

Fusion Propulsion: Field of the Future

As part of a mini-course on plasma for space propulsion IEEE ICOPS 2022, Seattle, WA, the potential use of controlled fusion is surveyed. Brief reviews are provided on space mission analysis and fusion technology for the respective nonspecialists. Notions for fusion propulsion are described for magnetic-, inertial-, and magneto-inertial confinement schemes. A system framework for a generic fusion rocket is provided, allowing comparison of possible fusion propulsion approaches with fission-driven electric rockets. The higher specific power offered by controlled fusion ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 5 kw/kg) versus <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 100 w/kg for fission or solar-powered systems suggests fusion can reduce trip times from years to months thereby enabling crewed missions to the outer planets.

Analysis of a higher-order vorticity confinement scheme in flux correction form

This article presents a detailed comparison of the classical source-term formulation of higher-order Vorticity Confinement with a flux-correction version, through an application to a series of well-documented cases. Both formulations and their numerical implementation are presented first. Then the methods are applied to the simple case of the long-time advection of an inviscid and isentropic vortex. A shock-vortex interaction case is also computed to demonstrate the compatibility of the method with the shock-capturing properties of the baseline scheme. Both methods are finally applied to a ZDES mode 3 (Wall-Modelled LES) simulation of a zero-pressure-gradient flat-plate turbulent boundary layer, showing a better preservation of smaller-scale vortical structures with respect to standard higher-order numerical schemes. Furthermore, the flux-correction form of Vorticity Confinement significantly improves the prediction of skin friction with respect to both the baseline scheme and the classical source-term formulation, thus showing that the flux-correction form of confinement is essential for a reliable prediction of this quantity.

Mechanical Properties of Rubberised Concrete Confined with Basalt-Fibre Textile-Reinforced Mortar Jackets

This paper presents an experimental investigation of the mechanical properties of rubberised concrete confined with basalt-fibre textile-reinforced mortar (TRM) jackets. The main aim is to evaluate the effectiveness of the TRM confinement scheme on cylindrical rubberised concrete specimens by examining five different mixtures (rubber content ranging from 10.5% up to 42% of the total aggregate volume), including a plain concrete reference mixture. Unconfined and confined specimens with either one or two TRM layers were subjected to monotonic axial loading. The results indicate a decrease in the compressive strength of unconfined concrete as the rubber content increased. The stress–strain curves of rubberised concrete became smoother at the peak as the rubber content increased, also exhibiting increased axial strain capacity post-peak. Rubberised concrete exhibited less brittle failure than plain concrete, accompanied by increased lateral dilation. Confinement with TRM increased the compressive strength, while also enhanced the performance in terms of toughness and axial deformation capacity compared to unconfined concrete. Overall, it is concluded that there is a promising potential for using TRM-confined rubberised concrete in applications with ductility demands and low environmental footprint specifications.

Experimental and numerical study of compressive behavior of axially loaded circular ultra-high-performance concrete-filled tube columns

To test the compressive behavior of ultra-high-performance fiber-reinforced concrete UHPFRC columns, numerical and experimental investigations were conducted using various confinement materials under axial compression loading. A total of seven columns were examined in the current experimental work. In this study, the major variables included the utilization of an outer steel tube, an inner steel tube, an outer polyvinyl chloride (PVC) tube, and an external wrap by CFRP, i.e., carbon fiber- reinforced polymer wrap. For UHPFRC-filled tube columns, a 3D finite element (FE) simulation has been developed. The commercial FE program ABAQUS was used. Moreover, validation against the obtained experimental results was carried out. The results showed that the outer steel tube had a better confinement impact on the given core concrete compared with the PVC tube and the CFRP sheet. The axial capacity of the column specimens confined with steel, PVC and CFRP was enhanced about 53 %, 13 %, 27 % compared to control specimens. All proposed confinement schemes improved the columns’ ductility and energy absorption considerably. Furthermore, the simulation results confirmed the reasonableness of the FE model of specimens to a significant extent; thus, they can be reliable to produce more predictions.

Path-Dependent Stress–Strain Model for FRP-Confined Recycled Brick Aggregate Concrete

Fiber-reinforced polymer (FRP) confinement has shown promise as an alternative method aimed at enabling the structural use of recycled brick aggregate concrete (RBAC) in columns. To facilitate practical applications, an existing stress–strain model for FRP-confined normal concrete is modified in this paper to extend its applicability to FRP-confined RBAC. The modification was based on a rigorous approach involving a direct examination of the path-independent assumption, which was made possible by conducting companion tests on actively confined and FRP-confined RBAC. Comparisons of the stress–strain and dilation responses obtained from the two confinement schemes showed that the axial strain of RBAC can be considered path-independent while the axial stress of RBAC tends to be path-dependent. The underlying cause is probably that the weak resistance of recycled brick aggregate (RBA) makes itself a medium for crack propagation. The effect of path dependence is accounted for in the modified model by purposefully weakening the stress–strain response of actively confined RBAC to correct the overestimate found in the axial stresses of FRP-confined RBAC, which originates from adopting the path-independent assumption.

Combined Dissipative and Hamiltonian Confinement of Cat Qubits

Quantum error correction with biased-noise qubits can drastically reduce the hardware overhead for universal and fault-tolerant quantum computation. Cat qubits are a promising realization of biased-noise qubits as they feature an exponential error bias inherited from their non-local encoding in the phase space of a quantum harmonic oscillator. To confine the state of an oscillator to the cat qubit manifold, two main approaches have been considered so far: a Kerr-based Hamiltonian confinement with high gate performances, and a dissipative confinement with robust protection against a broad range of noise mechanisms. We introduce a new combined dissipative and Hamiltonian confinement scheme based on two-photon dissipation together with a Two-Photon Exchange (TPE) Hamiltonian. The TPE Hamiltonian is similar to Kerr nonlinearity, but unlike the Kerr it only induces a bounded distinction between even- and odd-photon eigenstates, a highly beneficial feature for protecting the cat qubits with dissipative mechanisms. Using this combined confinement scheme, we demonstrate fast and bias-preserving gates with drastically improved performance compared to dissipative or Hamiltonian schemes. In addition, this combined scheme can be implemented experimentally with only minor modifications of existing dissipative cat qubit experiments.

Numerical investigations of the vortex feature-based vorticity confinement models for the assessment in three-dimensional vortex-dominated flows

In order to improve the vortex resolution in aerodynamic wakes, a locally normalized vortex feature-based vorticity confinement method is implemented into the multi-block, structured computational fluid dynamics solver (ROSITA). In this method, the second vorticity confinement (VC2) scheme with two well-known vortex feature detection methods (non-dimensional Q criterion, non-dimensional lambda _2 criterion) is employed to counterbalance the truncation error introduced by the numerical discretization of the convective term. The flow field of two benchmark three-dimensional steady vortex-dominated cases, the NACA0015 wing and the Caradonna–Tung hovering rotor, is simulated with the implemented method. The improvements in aerodynamics prediction, vorticity preservation, computational stability, and efficiency are demonstrated. From the numerical results, the vortex feature-based confinement models significantly improve the computational stability, the aerodynamic loads prediction and vorticity preservation capability, especially for the lambda _2–based VC2 model. In addition, it allows the use of higher confinement parameters on a coarse grid with a relatively higher computational efficiency to obtain better results than those of a finer grid.

Performance enhancement of AlGaN deep-ultraviolet laser diode using compositional Al-grading of Si-doped layers

Achieving high threshold current density and high optical confinement are big challenges in the realization of high-performance aluminum gallium nitride (AlGaN)-based deep-ultraviolet (DUV) laser diode (LD). In this work, compositional Al-grading of AlGaN layers is used to increase the optical confinement factor (OCF), carrier injection efficiency, gain, and emission power of the DUV LD. Compositional grading of waveguides (WGs) layer, electron blocking layer (EBL), and cladding layers (CLs) demonstrated that the device characteristic can be improved. By using compositional Al-grading of AlGaN p-WG, EBL, p-CL along with n-WG and n-CL, 17.4% OCF, 94.4 mW emission power, and 1369 m−1 gain at 267 nm peak emission wavelength are achieved. These improvements are attributed to the reduced threshold current density as well as using better optical confinement scheme in the DUV LD.